We have isolated a number of cloned monkey DNA fragments, some of which are believed to contain origins of DNA replication. Two of the fragments contain a class of moderately reiterated highly dispersed sequences known as the "O-family". We have been attempting to isolate a sequence-specific binding protein to these fragments. Another of the fragments contains the concensus sequence thought to be necessary for providing origin function for replication in yeast (the autonomously replicating or "ARS" sequence). The fragment has been cloned in yeast tester plasmids and does appear to have very weak ARS functions. We have sequenced a large portion of monkey mitochondrial DNA and compared it with the human sequence. We have prepared monoclonal antibody to DNA molecules containing cruciform structures. We have shown that the monoclonal antibody protects against the action of Endo VII but not single-stranded nucleases, suggesting that the antibody recognizes the base of the cruciform structure.